WATER APRIL 2014
134
Technical Papers
600kPa) and vacuum pressure gauges
(-100 to 0 kPa) (15). All gases produced
from the bioreactor exited via 0.45μm
air lters (16).
MEMBRANE MODULES
PTFE and PVDF membrane modules
were installed in both bioreactors.
Memcor hydrophilic hollow bre
PVDF membranes with a surface
area of 0.01m2, were used. The PVDF
membranes had an unknown pore size
and an outer diameter (OD) of 1.1
mm. Hydrophobic hollow bre PTFE
membranes with a surface area of
0.01m2, with an unknown pore size and
an outer diameter (OD) of 1.5mm, were
also used for this experiment. These
membranes were still under development
by the manufacturer and no further
information about the membranes could
be released at the time of the project.
MEMBRANE MODULES CLEANING
Chemical cleaning was applied to
the membrane modules between all
experiments. Cleaning was achieved by
removing the membrane modules from
the bioreactor and gently removing
the bio lm layers from the membrane
surface. Great care was taken not
to touch the membranes by hand
or damage them in any way.
Chemical cleaning was performed by
backwashing the membrane modules
with 10% v/v sodium hypochlorite.
The cleaning was performed outside
the bioreactor to ensure the microbial-
population was not negatively affected
by the sodium hypochlorite. The
membranes were also backwashed
several times with distilled water to
ensure all chemicals were removed
before reinstalment.
MEMBRANE FOULING RATE
Pressure gauge readings and ow
rate measurements were collected at
least twice a week. All readings and
measurements were completed exactly
20 minutes after the completion of a
backwash cycle. The membrane fouling
rate was based on the increase in
trans-membrane pressure over time.
However, because the peristaltic pumps
utilised in this project were not true
positive displacement pumps, the ow
rate decreased over time as the trans-
membrane pressure increased. For
this reason, the ux ( ow rate per unit
of membrane area) had to be used.
Membrane fouling rate in this experiment
was thus calculated as the increase of
trans-membrane pressure (kPa) per ux
(L/m2/h) per hour. Straight line
standard curves were generated
to indicate increases of membrane
fouling and were used to calculate the
membrane fouling rates. The gradients
of the standard curves were equal to the
membrane fouling rates.
SYNTHETIC WASTEWATER
FEEDING MEDIA
A synthetic wastewater medium was
used to feed the Anammox bioreactors
(Table 1). The composition of the
synthetic feed was used by Wang et
al. (2009), which was based on the
original synthetic media of Van de
Graaf et al. (1995). The concentrations
of ammonium sulphate and sodium
nitrate in the synthetic feed media
were slowly increased over the duration
of the project as nitrite and ammonia
consumption increased in the SMBRs.
SMBR INOCULATION
Anaerobic sludge from an industrial
wastewater treatment digester was
used to inoculate the bioreactors.
Previous Anammox bacteria have been
successfully isolated from wastewater
treatment plants (Sànchez-Melsió et
al., 2009). The seed originated from
anaerobic digesters with low levels of
COD and high levels of NH4. Small red
clusters in the seed sludge were also
observed under the microscope.
ANAMMOX OBSERVATIONS
The presence of Anammox bacteria
in the bioreactors was observed in
two ways: by physically observing the
biomass in the SMBRs over time under a
microscope and by monitoring the ratio
of nitrite and ammonia removal from
the bioreactors. Samples were observed
under an Olympus BH2 light microscope
and images were captured with a Canon
A410 digital camera every two weeks.
Observations of the amount, spread and
size of red cell clusters were recorded.
General observations of other micro-
organisms were also recorded.
The Anammox process utilises roughly
equal parts of ammonia and nitrite to
drive the reaction towards nitrogen
gas and water (Mulder et al., 1995;
Van de Graaf et al., 1995). Therefore,
equal amounts of ammonia and nitrite
removal from the bioreactors would
also indicate the presence of Anammox
activity. Therefore, water analyses
were performed weekly to monitor the
consumption of nitrite and ammonia from
the bioreactors. Ammonia, nitrite and
nitrate analysis were performed on the
in uent and ef uent of both systems.
WATER ANALYSIS
COD (Hach Method 2125925), ammonia
(Hach Method 10031), nitrite (Hach
Method 8153) and nitrate (Hach Method
8039) analyses were performed with
a Hach DR 5000 spectrophotometer,
using EPA approved methods. pH
measurements were performed on a
Hach SensIon 156 analyser and DO
measurements on a Hach HQ40D analyser.
RESULTS
BIOREACTOR OPERATING
CONDITIONS
An optimum Anammox growth
environment was maintained throughout
the project with a constant temperature
of 32˚C, pH between 8 and 8.5 and
stirring speed of 100±1 RPM in both
SMBRs. Biomass settled sludge volume
(SSV) remained between 15% and 20%
with hydraulic retention times between
3.0 and 3.5 days.
Table 1. Composition of synthetic wastewater feeding media for Anammox
SMBRs.
Major Salts
Trace Elements 1
Trace Elements 2
Distilled Water
1L
Distilled Water 1L Distilled Water 1L
(NH4)2SO4
0.50 g/L
EDTA
5 g/L
EDTA
15 g/L
NaNO2
0.50 g/L
FeSO4
5 g/L ZnSO4.7H2O 0.43 g/L
KHCO3
1.25 g/L
CoCl2.6H2O 0.24 g/L
KH2PO4
0.025 g/L
MnCl2.4H2O 0.99 g/L
MgSO4.7H2O
0.30 g/L
CuSO4.5H2O 0.25 g/L
CaCl2.2H2O
0.20 g/L
NaMoO4.2H2O 0.22 g/L
Trace elements 1 1.25mL
NiCl2.6H2O 0.19 g/L
Trace elements 2 1.25mL
NaSeO4.10H2O 0.21 g/L
H3BO4
0.014 g/L
NaWO4.2H2O 0.050 g/L
WASTEWATER TREATMENT